The present invention relates to a device for discriminating a light source illuminating a scene to be taken for use with a silver halide photographic camera, an electronic still camera, a video camera and the like. More particularly, the invention relates to a device which can discriminate a light source exactly at the time of taking the scene.
A scene to be taken is illuminated natural light, i.e. daylight, or by an artificial light such as a tungsten lamp, a fluorescent lamp, or a flash. Color reproduction is influenced by various characteristics of the light source, including color temperature spectral characteristics, and the like. Several methods have been known for reproducing the color of the object in an unchanged manner by removing the effect of the kind of light source. According to a conventional light source discriminating method in the field of silver halide photography, for example, the image recorded on a photographic film is subjected to photometry by a scanner mounted on a photographic printer in order to detect the color distribution from the three color photometric values thus obtained from each point. If the color distribution is regarded as a pattern peculiar to the fluorescent lamp, then the light source is judged to be a fluorescent lamp. If the distribution is regarded as a pattern of the tungsten lamp, the light source is judged to be a tungsten lamp. A color correction value is determined in accordance with the type of light source.
In a video camera or an electronic still camera, the white balance is adjusted to remove the influence of the color temperature of the light source. The gain values of the red and blue channels are adjusted while picking up a white object illuminated by light of the standard color temperature so that it is picked up electrically to be the achromatic color.
However, in the above-described method, in silver halide photography for discriminating a light source on the basis of color distribution, it is difficult to judge whether the color distribution is influenced by the illumination of the light source, or is dependent on the color of the object itself. The color also becomes different depending on the characteristic of the photographic film, so that the light source cannot be detected exactly. Even according to color correction by adjusting the white balance, the color of the reproduced image becomes different from that of the object under the influence of the spectral characteristics of the light source while the white balance is adjusted appropriately.